1. Field of the Invention
The present invention relates to a magnetostatic wave device and a material for use in the same.
2. Description of the Related Art
Magnetic garnet single crystals containing Fe has been used as materials for magnetostatic wave devices. In particular, a single crystal of Y.sub.3 Fe.sub.5 O.sub.12 (hereinafter referred to simply as "YIG") has a narrow ferromagnetic half-value width (.DELTA.H), which allows the difference between the input signal and the output signal to be small when the YIG is used in a magnetostatic wave device. As a result, YIG has been widely used.
That type of garnet single crystal is obtained as a film epitaxially grown on a substrate such as Ga.sub.3 Gd.sub.5 O.sub.12 (hereinafter referred to simply as "GGG") by, for example, a liquid phase epitaxial growth process.
A magnetostatic wave device using a YIG single crystal operates at a frequency of about 2 GHz. However, in the case where a magnetostatic wave device is employed in a noise filter used in a broadcast satellite (BS) tuner, the magnetostatic wave device is required to operate at a frequency in the range of from several hundreds MHz to several hundred thousands MHz.
When the magnetostatic forward volume wave (MSFVW) mode is selected in the magnetostatic wave (MSW) mode, the operating frequency of the device is expressed by eq.(1). EQU .omega.=.gamma.(H.sub.ex -N.multidot.4.pi.Ms) (1)
where
.omega.: frequency PA1 .gamma.: gyromagnetic ratio PA1 H.sub.ex : applied magnetic field PA1 N: demagnetization coefficient PA1 4.pi.Ms: saturation magnetization PA1 H.sub.i : internal magnetic field PA1 H.sub.ex : applied magnetic field PA1 N: demagnetization coefficient PA1 4.pi.Ms: saturation magnetization PA1 H.sub.a : anisotropic magnetic field
When the magnetostatic surface wave (MSSW) mode is used, the operating frequency of the device is expressed by eqs.(2) and (3). EQU .omega.=.gamma.{H.sub.i (H.sub.i +4.pi.Ms)}.sup.1/2 (2) EQU H.sub.i =H.sub.ex -N.multidot.4.pi.Ms+H.sub.a ( 3)
where
Accordingly, the external magnetic field or the saturation magnetization needs to be decreased in order to decrease the operating frequency of a magnetostatic wave device.